Inhibition of methanogenesis by methyl fluoride: studies of pure and defined mixed cultures of anaerobic bacteria and archaea.

Methyl fluoride (fluoromethane [CH(inf3)F]) has been used as a selective inhibitor of CH(inf4) oxidation by aerobic methanotrophic bacteria in studies of CH(inf4) emission from natural systems. In such studies, CH(inf3)F also diffuses into the anaerobic zones where CH(inf4) is produced. The effects of CH(inf3)F on pure and defined mixed cultures of anaerobic microorganisms were investigated. About 1 kPa of CH(inf3)F, similar to the amounts used in inhibition experiments, inhibited growth of and CH(inf4) production by pure cultures of aceticlastic methanogens (Methanosaeta spp. and Methanosarcina spp.) and by a methanogenic mixed culture of anaerobic microorganisms in which acetate was produced as an intermediate. With greater quantities of CH(inf3)F, hydrogenotrophic methanogens were also inhibited. At a partial pressure of CH(inf3)F of 1 kPa, homoacetogenic, sulfate-reducing, and fermentative bacteria and a methanogenic mixed culture of anaerobic microorganisms based on hydrogen syntrophy were not inhibited. The inhibition by CH(inf3)F of the growth and CH(inf4) production of Methanosarcina mazei growing on acetate was reversible. CH(inf3)F inhibited only acetate utilization by Methanosarcina barkeri, which is able to use acetate and hydrogen simultaneously, when both acetate and hydrogen were present. These findings suggest that the use of CH(inf3)F as a selective inhibitor of aerobic CH(inf4) oxidation in undefined systems must be interpreted with great care. However, by a careful choice of concentrations, CH(inf3)F may be useful for the rapid determination of the role of acetate as a CH(inf4) precursor.